More than 5m British households have been overcharged by gas suppliers such as E.ON and British Gas to the tune of £454m, according to a new survey.

They are owed an average of £89 because many companies have not reduced their direct debit charges after cutting tariffs this year, claims comparison site moneysupermarket.com. More than four million of the affected households have not asked for their cash back, resulting in £363m being unclaimed.

Almost 2m other households were in debt to their suppliers by an average of £151 – a total of £280m – the survey found. But that means that overall, suppliers owe British consumers £174m.

Scott Byrom, utilities manager at moneysupermarket.com, said: "In 2008 we saw gas giants holding £225m of their customers' cash 'on float' and while it is encouraging to see this has decreased by more than £50m this year, there is still cause for concern. This year bill payers have welcomed price cuts on online energy tariffs across the board; however it's unsurprising customers are still finding themselves in credit with their gas supplier, as direct debit arrangements may not have been updated to reflect these price changes."

Trade group the Energy Retail Association said that it was normal for consumers to be in credit towards the end of the summer, when they had used less energy.

It said: "This research is misleading as it doesn't reflect the fact that people use different amounts of energy at different times of the year. So it is common for customers to be in credit towards the end of the summer, when they have used less energy, and then to owe their energy company money during the winter months when they have the heating on and use more energy.

"People like being able to choose how they pay and a regular direct debit payment keeps bills relatively stable over the course of the year and helps people to budget. Customers can of course at any time request a refund or pay off any money they owe."